title: Influence of imaging parameters, flow velocity, and pulsatile flow on three-dimensional time-of-flight MR angiography: experimental studies.
abstract: OBJECTIVE
  The purpose of this study is to evaluate the influence of imaging parameters (TR and flip angle), velocity and pulsatility of flow on three-dimensional time-of-flight magnetic resonance (3D TOF MR) angiography by using a flow phantom.
  
  
  METHODS
  The 3D TOF MR angiography of a flow phantom was performed at 1.5-T with various TRs, flip angles and flow velocity. The influence of pulsatile flow was also evaluated.
  
  
  RESULTS
  The imaging parameters and flow velocity affected the saturation effects of inflowing spins. Signal loss due to saturation of inflowing spins was more pronounced with a shorter TR, larger flip angle, or lower flow velocity. However signal intensity of stationary tissue were more suppressed with a shorter TR resulting in a larger signal difference to noise ratio of the flowing fluid. Velocity of the flow also affected the signal loss due to intravoxel phase dispersion, which was apparently observed with a stenotic tube. Pulsatility of flow resulted in decreased intensity of flowing fluid and in ghost artifacts along the phase-encoding and slice-select directions. The spacing between these ghosts and intensity of them were dependent on TR, flip angle and pulse rates.
  
  
  CONCLUSIONS
  Understanding the influence of imaging parameters and flow characteristics is essential for evaluating the MR angiograms or for improving their quality.
authors.affiliation: Department of Radiology, Miyazaki Medical College, Japan. tkodama@post1.miyazaki-med.ac.jp
authors.forename: T
authors.initials: T
authors.lastname: Kodama
authors.forename: K
authors.initials: K
authors.lastname: Watanabe
mesh_terms: D001783:Blood Flow Velocity; D018810:Magnetic Resonance Angiography; D019047:Phantoms, Imaging; D011673:Pulsatile Flow